S6 THE EVOLUTION OF MAN. 



functions or actions of the organs themselves, from the 

 exercise or absence of exercise, the use or disuse of these 

 organs. To mention examples, the "Woodpecker and the 

 Humming-bird owe their peculiarly long tongue to their 

 habit of using these organs to take their food out of 

 narrow and deep crevices ; the Frog acquired a web between 

 its toes from the motions of swimming ; the Giraffe gained 

 its long neck by stretching it up to the branches of trees. 

 Habits, the use and disuse of organs, are certainly of the 

 greatest importance as efficient causes of organic form ; but 

 they are insufficient to explain the modification of species. 

 As a second and equally important cause, Lamarck fully 

 perceived that Heredity must necessarily co-operate with 

 Adaptation. He maintained that the variations of organs 

 arising from habit or use are in themselves at first but 

 insignificant in each separate individual ; but that by the 

 accumulation of the effects produced in each individual, 

 transmitted from generation to generation in an ever increas- 

 ing number, they become very significant. This was quite 

 a correct fundamental idea ; but Lamarck did not reach the 

 principle which Darwin subsequently introduced as the 

 most important factor in the Theory of Transmutation, 

 namely, the principle of Natural Selection in the Struggle 

 for Existence. Lamarck failed to discover this most im- 

 portant causal relation, and this, together with the low 

 condition of all biological sciences at that time, prevented 

 him from more firmly establishing his theory of the common 

 descent of animals and man. 



Lamarck also attempted to explain the evolution of Man 

 from*the Ape, as principally due to the progress made by 

 the Ape in its habits of life, the further development and 



